Optical film and liquid-crystal display device

Abstract

An optical film has a transparent film, an adhesive layer provided on one surface of the transparent film, the adhesive layer having a refractive index different by 0.1 or less from that of a layer of the one surface of the transparent film, and a repetitive prismatic structure provided on the other surface of the transparent film, the repetitive prismatic structure having optical path changing slopes aligned in a substantially constant direction at an inclination angle in a range of from 35 to 48 degrees with respect to a plane of the transparent film. Another optical film has a transparent film having an average in-plane retardation of not larger than 30 nm, an adhesive layer provided on one surface of the transparent film, the adhesive layer having a refractive index different by 0.12 or less from that of a layer of the one surface of the transparent film, and the repetitive prismatic structure provided on the other surface of the transparent film. Still another optical film has a transparent film having a refractive index of not lower than 1.49, a transparent adhesive layer provided on one surface of the transparent film, the transparent adhesive means having a refractive index of not lower than 1.49, and the repetitive prismatic structure provided on the other surface of the transparent film.

What is claimed is:  
     
       1. An optical film comprising: 
       a transparent film comprising at least one layer forming at least one surface of said transparent film;  
       an adhesive layer provided on said one surface of said transparent film, said adhesive layer having a refractive index different by 0.1 or less from a refractive index of said at least one layer of said transparent film; and  
       a repetitive prismatic structure provided on the other surface of said transparent film, said repetitive prismatic structure having optical path changing slopes at least a portion of which are aligned in a substantially constant direction at an inclination angle in a range of from 35 to 48 degrees with respect to a plane of said transparent film,  
       wherein a projected area, onto said film plane, of flat surfaces each having an inclination angle of not larger than 5 degrees with respect to said film plane is not smaller than 10 times as large as a projected area, onto said film plane, of the slopes each having an inclination angle of not smaller than 35 degrees with respect to said film plane.  
     
     
       2. An optical film according to  claim 1 , wherein said optical path changing slopes are constituted by at least two kinds of slopes in which one kind of slopes aligned in a substantially constant direction serve as a reference while the other kind of slopes are aligned substantially in a direction which is opposite to said one kind of slopes; and wherein said adhesive layer is covered with a strip sheet. 
     
     
       3. An optical film according to  claim 1 , wherein said inclination angle of each of said optical path changing slopes with respect to said film plane is in a range of from 38 to 45 degrees. 
     
     
       4. An optical film according to  claim 1 , wherein said optical path changing slopes are formed based on a structure of grooves each shaped substantially like an isosceles triangle or any other triangle in section. 
     
     
       5. An optical film according to  claim 1 , wherein said optical path changing slopes are formed based on a structure of grooves or protrusions each shaped substantially like a tetragon or a pentagon in section. 
     
     
       6. An optical film according to  claim 1 , wherein said prismatic structure includes optical path changing slopes each having an inclination angle in a range of from 38 to 45 degrees with respect to said film plane, and flat surfaces each having an inclination angle of not larger than 5 degrees with respect to said film plane; wherein a projected width of each of said flat surfaces onto said film plane is not smaller than 10 times as large as a projected width of each of said optical path changing slopes onto said film plane; and wherein said prismatic structure is formed into continuous grooves each of which is shaped substantially like a triangle in section and each of which is extended from one end of said film to the other end thereof. 
     
     
       7. An optical film according to  claim 1 , wherein said prismatic structure having optical path changing slopes is formed into discontinuous grooves each shaped substantially like a polygon in section; wherein a length of each of said discontinuous grooves is not smaller than five times as large as a depth of each of said discontinuous grooves; wherein said optical path changing slopes are formed in a direction of the length of said grooves at an inclination angle in a range of from 38 to 45 degrees with respect to said film plane; and wherein a projected area of said discontinuous grooves onto an area of said film plane is not larger than 10%. 
     
     
       8. An optical film according to  claim 7 , wherein said discontinuous grooves each are shaped substantially like a triangle in section. 
     
     
       9. An optical film according to  claim 7 , wherein said discontinuous grooves each are shaped substantially like a tetragon or pentagon in section. 
     
     
       10. An optical film according to  claim 1 , wherein said transparent film is not thicker than 300 μm. 
     
     
       11. An optical film according to  claim 1 , further comprising a reflection layer disposed closely on a surface of said transparent film on which said prismatic structure having said optical path changing slopes is formed. 
     
     
       12. An optical film according to  claim 1 , wherein ridgelines of said optical path changing slopes are parallel to or inclined within an angle range of ±30 degrees with respect to one side of said transparent film. 
     
     
       13. An optical film according to  claim 1 , wherein said adhesive layer is of a light diffusion type.